I finally managed to read the Nightwish book by Mape Ollila. It had quite many pieces of information that I had totally missed, like that the band gave the last warning to Tarja etc. It felt incredible how they managed to let the band athmosphere decrease to such a horrible level in 2004-2005.
Especially if you compare it with Dream Theater and the events leading to MP's departure in 2010. I got the feeling from the book that if Tarja had got a good record deal in 2004 or later, she would have quit Nightwish immediately. But thanks to her husband's lack of business skills, the deal was not achieved and the band decided to get rid of them proactively.
So although there were some similarities to DT situation, I don't think things would have got so bad in DT even if MP hadn't got the lucrative chance of joining A7X in 2010. Although the relationships in DT were a bit strained, MP still cared for the band, acted professionally and did not try to sabotage the band as Tarja Turunen / Marcelo Cabuli did. And as DT members are American, they are capable of communication and can perhaps even make amends and forget old disagreements
On the other hand, seeing how they've completely misfired choosing their previous singer, even though it took them awhile (it was a sort of a "we totally trust her she'll be able to nail old songs based on a few rehearsals, and she has a kid already and might want more and she's never toured but she'll totally be able to handle world tour after world tour"-deal), maybe it would be good for them to first do a full tour with Floor to see if they want to stick with her for the rest of their career.
This is also what I don't fully get. I understood from the book that the problems in Nightwish kind of started when Tarja was unhappy when touring -> did not communicate or spend time with the band -> spent time with Marcelo -> etc. So one would think that singers with a proven track record in touring would be given precedence in the selection process. The other complaint that the band members had for Tarja was lack of dedication to the band. So again it seems a bit odd to have a frontwoman who is raising a large family. But hey, if it works for Within Temptation, so why not for Nightwish as well?